A6 (G8) Downshift Timing Pull how to get rid of it..

[johnh]

Several of us see a huge timing pull on downshifts, even with Power Downshift TQM disabled. In fact if you look at the scans there's really no difference with it enabled vs. disabled.

There seems to be no way to stop this from happening. The Trans TQM basically pulls all timing for about 1 second on a 6-2 downshift. This of course makes for a solid 15 sec car experience from a roll--in other words a turd.

Anyone tune this out? I can't find anything to lower it. Basically I would hope for a Shift Torque Factor like table(s) for downshifting and let us control or limit this.

Are you Vette guys seeing this too?

[8850]

If you find out I would like to know. I'm not sure there is any control in out tuners for that 6-2 or 5-2 downshift. If you go WOT from 4th (less than 25 mph) downshift is like it's suppose to be but once into 5th we get that 1 second hesitation.

[LSX378]

Any A6's that do with zero or near zero downshift period?

I'd bet it is still quicker than an equivalent downshift in an M6.

[johnh]

I'd bet it is still quicker than an equivalent downshift in an M6.

I bet not. After the shift, you get 0 to -5 timing for 1 second or until about 4100 rpm. In an M6 you'd have to hold the clutch in for 1 second to get the same. Its so bad that it makes it feel like the engine is bogging.

And its definitely trans TQM telling the ECM to pull the power.

[LSX378]

Oh yes, definately the trans telling the engine to reduce torque.

When you shift an M6, the cut in power runs from when the foot lifts off the accelerator pedal not when the clutch is pushed in. It may seem quick but still takes more than a second for a 5-2 downshift. Autos seems slower because your brain isnt occupied with moving an accel pedal, clutch pedal and navigating a gearstick back through nuetral to 2nd.

The engine goes to zero power in a manual duriing the shift.

When you say "after the shift" do you mean after the period the shift timing counter runs for?

One way around this is to limit the ECM minimum spark timing...but it looks like that table is not there.

[04blackgmc]

yes after the shift is done there is still a timing for for some time...

let me look at a log and tell ya

[04blackgmc]

ok looking at a log i went from 5-2
went from 25-26* of timing at 2.994 SEconds at around 2100 rpms
lowest timing got was -7.5 so thats 25* drop with another 7.5 on top of that
regained timing at 4.039 seconds at 4800 rpms

[madvette08]

Neutral down skip is the culprit.

Ian

[8850]

Neutral down skip is the culprit.

Ian

Don't think NDS is the culprit Ian. Here are my tests from this morning with Neutrial Down Skip disabled and then enabled. Both tests were started with tranny in 5th gear.

Log 1 is with NDS diabled. Note engagement of first gear at frame 49. At frame 109 timing has resumed back to 26*. 1.359 seconds to resume power.

In log 2 with NDS enabled. First gear engagement begins at frame 56. Full timing of 26* resumes at frame 109. 1.329 seconds. Actually slightly quicker than with NDS disabled.

I exported to Microsoft spreadsheet to count the frames so count will be slight off reading direct but still shows the difference.

Any more ideas?

[johnh]

Don't think NDS is the culprit Ian.

I've tried that same test with similar results--it didn't help.

[Bill@HPTuners]

This is what our head engineer had to say

the problem is the 6-2 shift is a shift via neutral, the TCM uses aggressive tqmgt to prevent engine flare while the trans is in neutral. It can be turned off by:
- set Neutral Down Skip, Disabled
- Speed Ctrl Terminate, Immediate

Also set Limit TqMgt Enable Temp to something high

[04blackgmc]

This is what our head engineer had to say

hmmm
well
ive had Speed Ctrl Terminate, Immediate set for awhile like that
Also set Limit TqMgt Enable Temp to something high like he said i had it at 200 i never let my tranny peak over 185..

never messed with the Neutral Down Skip maybe all 3 together solve the problem..

but i think this precaution is a good thing for the tranny as my tranny tunes progress from what i had i like to think they are getting easier on the tranny yet still yield good results.

[johnh]

Thanks Bill!

[8850]

This is what our head engineer had to say

Have not tried all three of those at the same time. What I would prefer however is to just shorten the downshift time, not take it to zero. Something on the order of the way it shifts stock from 4-1, about .4-.5 seconds. Do appreciate the info Bill!

[Sneakyws6]

I had the NDS for awhile set to disabled and the speed control to immediate and all I noticed were the brutal downshifts.

[johnh]

I tried all three set as indicated. Downshifts were a bit harsh and unfortunately the timing pull was still there--so those settings didn't work or help.

Any more ideas?

[johnh]

Here's the tune and scan.

It feels like this: Floor it, it pulls timing torque, first for Dod (if on), then trans, then it shifts--completes the shift, and then keeps the timing out till it hits 4000 rpm or so (usually about 1 sec).

I'd like to keep some of the TQM on during the shift, but shorten the timing pull duration and amount ( put full timing back at say 2500 rpms instead).

Either way it seems we don't have access to the params that drive this.

[Chris@HPTuners]

the tune still has Power Downshift Tq Reduction enabled.

also set the limit tq mgt Enable Temp to something very high

set all the tip-in, flare tqmgt options to None.

[8850]

the tune still has Power Downshift Tq Reduction enabled.

also set the limit tq mgt Enable Temp to something very high

set all the tip-in, flare tqmgt options to None.

Something like this Chris?

[Chris@HPTuners]

yes, also set your TCC max torque to a high number.

also, you know you can resize the window so the scrollbars aren't there